A general sklearn dependency update

[saattrupdan]

This is an attempt to collect all the sklearn dependency issues currently present.

Presort parameter
The parameter 'presort' is deprecated and has no effect. It will be removed in v0.24. You can suppress this warning by not passing any value to the 'presort' parameter.
See also: #85
Solution: Remove presort parameter when calling BaseDecisionTree.

Joblib
C:\Users\natha\Miniconda3\envs\ml\lib\site-packages\sklearn\externals\joblib\__init__.py:15: DeprecationWarning: sklearn.externals.joblib is deprecated in 0.21 and will be removed in 0.23. Please import this functionality directly from joblib, which can be installed with: pip install joblib.
See also: #81
Solution: Use joblib directly, rather than sklearn.externals.joblib.

Six
C:\Users\natha\Miniconda3\envs\ml\lib\site-packages\sklearn\externals\six.py:31: DeprecationWarning: The module is deprecated in version 0.21 and will be removed in version 0.23 since we've dropped support for Python 2.7.
See also: #81
Solution: Replace sklearn.externals.six with six.

Ensemble and tree
/home/leidem/gitsky/streetwise-model/venv/lib/python3.7/site-packages/sklearn/utils/deprecation.py:144: FutureWarning: The sklearn.ensemble.forest module is deprecated in version 0.22 and will be removed in version 0.24. The corresponding classes / functions should instead be imported from sklearn.ensemble. Anything that cannot be imported from sklearn.ensemble is now part of the private API.
/home/leidem/gitsky/streetwise-model/venv/lib/python3.7/site-packages/sklearn/utils/deprecation.py:144: FutureWarning: The sklearn.tree.tree module is deprecated in version 0.22 and will be removed in version 0.24. The corresponding classes / functions should instead be imported from sklearn.tree. Anything that cannot be imported from sklearn.tree is now part of the private API.
Solution: Replace sklearn.ensemble.forest by sklearn.ensemble, and sklearn.tree.tree by sklearn.tree.

Testing
FutureWarning: The sklearn.utils.testing module is deprecated in version 0.22 and will be removed in version 0.24. The corresponding classes / functions should instead be imported from sklearn.utils. Anything that cannot be imported from sklearn.utils is now part of the private API.
Solution: Replace sklearn.utils.testing with sklearn.utils.

[saattrupdan]

Implemented the above and more in #89

[saattrupdan]

Given that this package does not seem to be maintained, I have forked the quantile regression forest bit of the code into my doubt package, https://github.com/saattrupdan/doubt, if that's of any interest to folks.